The invention relates to a method and apparatus for the application of a coating material such as pressure sensitive adhesive, to individual sheets, such as sheets of paper.
It is desirable in some fields to apply pressure sensitive adhesive to a paper substrate and several methods are known for performing this process. German patent application 36 06 199, for example, discloses a method and apparatus for applying pressure sensitive adhesive on a continues web of paper. The web is coated with a primer, or adhesion promoter and dried in a first drying station. Next, an optional low adhesion backsize, or release layer, may be coated onto the opposite surface of the web and dried at a second drying station. Finally, a circulating intermediate carrier applies the pressure sensitive adhesive, which has been partially dried while on the intermediate carrier, over the primer layer. The paper web may then be collected and further processed as desired.
The various drying steps disclosed in the ""199 patent (drying the primer layer, drying the low adhesion backsize layer, and drying the adhesive layer while on the intermediate carrier) remove moisture from the aqueous primer, backsize and adhesive materials, to prevent the paper web from curling or wrinkling. However, the sequential application and drying of the primer and low adhesion backsize layers typically result in some curling of the paper web, which is undesirable. The curling problem would be more pronounced in the context of the application of a primer, low adhesion backsize, and adhesive to individual paper sheets rather than a paper web, because the web is typically in tension whereas the individual sheets are not. Thus, the method and apparatus of the ""199 patent typically is not suitable for use with individual paper sheets.
It is therefore desirable to provide a method and apparatus for applying primer, low adhesion backsize, and pressure sensitive adhesive to a plurality of individual paper sheets without inducing curling or cockling of the sheets.
The present invention includes within its scope an apparatus for applying a coating material to a plurality of sheets as the sheets are conveyed past the apparatus. The apparatus comprises means for supplying a plurality of sheets, means for overlapping the sheets, such that a minor portion of each sheet overlies a portion of an adjacent sheet, and a minor portion of each sheet underlies a portion of a second adjacent sheet, a coating station comprising means for receiving coating material from a supply of such material, and for applying the coating material to a first major surface of the overlapping sheets as the sheets are conveyed past the coating station, and means for collection the coated sheets. In one embodiment, the coating material is a pressure sensitive adhesive, and the sheets are sheets of paper.
Also provided is a method of applying a coating material to a plurality of sheets. The method comprises the steps of providing a plurality of sheets, overlapping the sheets, such that a minor portion of each sheet overlies a portion of an adjacent sheet, and that a minor portion of each sheet underlies a portion of a second adjacent sheet, providing a source of coating material, applying a coating material to a first major surface of the overlapping sheets as the sheets are conveyed past the coating station, and collecting the coated sheets. In one embodiment of the inventive method, the coating material is a pressure sensitive adhesive, and the sheets are sheets of paper. Also provided is a sheet coated with a coating material according to the foregoing method.